Regioselective Synthesis of Phosphonylated Sugars from Reactions of Glycals with Diphenylphosphenium Cation

Reaction of methyl 4,6‐di‐O‐acetyl‐2,3‐dideoxy‐d‐erythro‐hex‐2‐enopyranoside 1 with two equivalents of diphenylphosphenium cation at 0°C gave the 1‐phosphonylated 2‐enopyranosides 3α and 3β as major products. Similarly, reaction of diphenylphosphenium cation with tri‐O‐acetylglycal afforded the same products in a similar ratio. In contrast, a reaction with tri‐O‐benzylglucal at reflux temperature of dichloromethane afforded the 3‐phosphonylated sugar 13 as a major product. These reactions may proceed via stable allyl cations.